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Unit 2: Weather Dynamics
Chapter 1: Hydrological Cycle
Science 10
Mrs. Purba
UNIT 2 Chapter 1: Inquiring about Weather
Importance of H2O• From the beginning of time when water
first appeared, it has been constant in
quantity and continuously in motion.
• Little has been added or lost over the
years.
• The same water molecules have been
transferred time and time again from the
oceans and the land surface into the
atmosphere by evaporation, dropped on
the land as precipitation, and transferred
back to the sea by rivers and
groundwater.
• This endless circulation is known as the
"hydrologic cycle" or as the "water
cycle".
UNIT 2 Chapter 1: Hydrological Cycle Section 1.1
UNIT 2 Chapter 1: Hydrological Cycle Section 1.1
•The illustration shows the hydrologic cycle in which water leaves the atmosphere
and falls to earth as precipitation where it enters surface waters or percolates into
the water table and groundwater and eventually is taken back into the atmosphere
by transpiration and evaporation to begin the cycle again. There are 9
components to remember.
UNIT 2 Chapter 1: Hydrological Cycle Section 1.1
•1. Evaporation
As water is heated by the sun, surface molecules become sufficiently energized to
break free of the attractive force binding them together, and then evaporate and
rise as invisible vapour in the atmosphere.
UNIT 2 Chapter 1: Hydrological Cycle Section 1.1
2. Transpiration
Water vapour is also emitted from plant leaves by a process called transpiration.
Every day an actively growing plant transpires 5 to 10 times as much water as it
can hold at once.
UNIT 2 Chapter 1: Hydrological Cycle Section 1.1
3. Condensation
As water vapour rises, it cools and eventually condenses, usually on tiny particles
of dust in the air. When it condenses it becomes a liquid again or turns directly into
a solid (ice, hail or snow). These water particles then collect and form clouds.
UNIT 2 Chapter 1: Hydrological Cycle Section 1.1
4. Precipitation
Precipitation in the form of rain, snow and hail comes from clouds. Clouds move
around the world, propelled by air currents. For instance, when they rise over
mountain ranges, they cool, becoming so saturated with water that water begins to
fall as rain, snow or hail, depending on the temperature of the surrounding air.
UNIT 2 Chapter 1: Hydrological Cycle Section 1.1
5. Runoff
Excessive rain or snowmelt can produce overland flow to creeks and ditches.
Runoff is visible flow of water in rivers, creeks and lakes as the water stored in the
basin drains out.
UNIT 2 Chapter 1: Hydrological Cycle Section 1.1
6. Percolation or Infiltration
Some of the precipitation and snow melt moves downwards, percolates or
infiltrates through cracks, joints and pores in soil and rocks until it reaches the
water table where it becomes groundwater.
UNIT 2 Chapter 1: Hydrological Cycle Section 1.1
7. Groundwater
Subterranean water is held in cracks and pore spaces. Depending on the
geology, the groundwater can flow to support streams. It can also be tapped by
wells. Some groundwater is very old and may have been there for thousands of
years.
UNIT 2 Chapter 1: Hydrological Cycle Section 1.1
8. Water table
The water table is the level at which water stands in a shallow well.
UNIT 2 Chapter 1: Hydrological Cycle Section 1.1
9. The Sun-Powered Cycle (Radiation)
Heating of the ocean water by the sun is the key process that keeps the
hydrologic cycle in motion. Water evaporates, then falls as precipitation in the
form of rain, hail, snow, sleet, drizzle or fog. On its way to Earth some precipitation
may evaporate or, when it falls over land, be intercepted by vegetation before
reaching the ground.
The cycle continues in three different ways:
1. Evaporation/transpiration –
• On average, as much as 40 percent
of precipitation in Canada is
evaporated or transpired.
UNIT 2 Chapter 1: Hydrological Cycle Section 1.1
The cycle continues in three different ways:
2. Percolation/Infiltration into the ground
• Water moves downward through cracks and pores in soil and rocks
to the water table.
• Water can move back up by capillary action or it can move vertically
or horizontally under the earth's surface until it re-enters a surface
water system.
UNIT 2 Chapter 1: Hydrological Cycle Section 1.1
The cycle continues in three different ways:
3. Surface runoff
• Water runs overland into nearby
streams and lakes
• the steeper the land and the less
porous the soil, the greater the
runoff.
UNIT 2 Chapter 1: Hydrological Cycle Section 1.1